Triglyceride-rich proteins (TRL) consist of a great variety of lipoproteins differing in size, density, and apolipoprotein content. Based on their size and ability to enter the arterial wall, certain TRLs are considered atherogenic while others are not. Remnant lipoproteins, which are considered atherogenic, consist of partially catabolized intestinal chylomicrons or hepatic very low density lipoproteins (VLDLs) that are reduced in size, partially depleted of triglycerides, and enriched with cholesteryl esters. Remnant lipoproteins are also referred to as intermediate density lipoproteins (IDLs) based on how they separate on ultracentrifugation; IDLs are lipoproteins with a density that falls between low density lipoproteins (LDLs) and VLDLs.

Measurement of IDLs has been technically difficult and largely confined to a research setting because IDLs vary in size and contain varying proportions of triglycerides and cholesterol, with no available direct method of testing. However, recently, an immunoseparation assay has received approval from the U.S. Food and Drug Administration (FDA) for the direct measurement of IDL. Measurement of IDLs has been investigated in 2 settings:

As a tool for risk assessment for coronary heart disease

IDLs are considered atherogenic, and a variety of studies have suggested that IDL are associated with an increase in coronary heart disease risk; e.g., elevated IDLs may be a predictor of progression of coronary atherosclerosis and coronary events. Elevated IDLs may also be associated with a high triglyceride level (from 200-499 mg/dL), which is also a cardiac risk factor.

As a technique to diagnose type III hyperlipoproteinemia (also called dysbetalipoproteinemia)

Type III hyperlipoproteinemia is an uncommon familial disorder characterized by tuboeruptive and pathognomonic planar xanthomas and a marked predisposition to severe premature atherosclerosis. The disorder is characterized by elevated plasma cholesterol and trigylceride levels, both typically greater than 300 mg/dL. The hyperlipidemia is caused by the accumulation of remnant lipoproteins. Receptor-binding defective forms of apolipoprotein E are typically found. Apo E mediates binding of remnant lipoproteins to their hepatic receptors, and, therefore, when dysfunctional apo E is present, these remnants accumulate in the plasma. Diagnosis of this abnormality is usually based on apo E pheno- or genotyping.

Policy

Each benefit plan, summary plan description or contract defines which services are covered, which services are excluded, and which services are subject to dollar caps or other limitations, conditions or exclusions. Members and their providers have the responsibility for consulting the member's benefit plan, summary plan description or contract to determine if there are any exclusions or other benefit limitations applicable to this service or supply. If there is a discrepancy between a Medical Policy and a member's benefit plan, summary plan description or contract, the benefit plan, summary plan description or contract will govern.

Coverage

Measurement of serum intermediate density lipoproteins, also referred to as remnant-like particles, is considered experimental, investigational and unproven.

Rationale

Measurement of intermediate density lipoproteins (IDLs) has been widely investigated as a cardiac risk factor, principally in an effort to further understand the association between triglycerides and cardiac risk. For example, triglycerides are carried in virtually all plasma lipoprotein and thus are highly heterogeneous. Triglycerides may also carry a different risk when present in the postprandial or fasting state. Thus the relationship between plasma triglycerides and cardiac risk is extremely complex. It has been hypothesized that serum levels of remnant lipoproteins, i.e., IDLs, may be a more specific cardiac risk factor compared to triglycerides per se. A variety of epidemiologic studies have been published that have compared the cardiac risk associated with triglycerides and IDLs. For example, in 1999, Kugiyama and colleagues measured remnant lipoprotein levels in 135 patients with coronary artery disease (CAD). (1) Patients were followed up for 3 years for additional clinical coronary events, such as revascularization procedures, nonfatal myocardial infarction, or cardiac death. The study demonstrated that higher levels of remnant lipoproteins in the fasting serum predicted the development of clinical coronary events in patients with CAD independently of other risk factors. Other studies using indirect measurements of IDLs have also shown that serum IDL levels are independently correlated with coronary artery lesion progression, as evidenced by serial cardiac imaging and clinical events. A representative sample is referenced. (2-5)

While measurement of IDLs has emerged as an important research tool in evaluating cardiac risk factors and understanding how different components of plasma triglycerides contribute to cardiac risk, it is unclear how the management of IDLs can be used in the management of the patient. As noted in a prior Technology Evaluation Center (TEC) special report on high-sensitivity C-reactive protein, improved risk prediction does not by itself result in better health outcomes. (6) To improve outcomes, clinicians must have the tools to translate this information into clinical practice. Management of cardiac risk factors is largely based on the recommendations of the National Cholesterol Education Program, which published the Adult Treatment Panel III Report in May 2001. (7) ATP III defines target levels of LDL cholesterol based on risk as assessed by measurements of LDL cholesterol, total cholesterol, and HDL cholesterol, in addition to other factors, such as history of cigarette smoking, hypertension, family history of premature coronary heart disease, and age. The LDL cholesterol level may be reduced by diet, exercise, and various pharmacologic therapies, most prominently HMC-CoA reductase drugs, also referred to as statins. The ATP III also identified borderline (150–99 mg/dl), high (200–499 mg/dl), and very high triglyceride levels (>500 mg/dl) and suggested treatment strategies for those with high triglycerides. For example, patients with elevated triglycerides typically have an associated increase in remnant lipoproteins, which are reflected by higher serum levels of VLDL remnants. The ATP III guidelines suggest that in patients with high triglycerides, "VLDL cholesterol can be added to LDL cholesterol to become a secondary target of therapy. VLDL + LDL, termed non-HDL cholesterol, equals total cholesterol minus HDL cholesterol. A normal VLDL cholesterol can be considered to be a level <30 mg/dL. Thus a therapeutic goal for non-HDL cholesterol can be 30 mg/dL higher than the goal for LDL cholesterol." Suggested treatment of elevated triglycerides focuses on changes in life habits, such as body weight control, regular physical activity, smoking cessation, restriction of alcohol use, and avoidance of high carbohydrate diets. Pharmacologic therapy focuses on statin drugs or nicotinic acid. The ATP III supporting document includes the following discussion of remnant lipoproteins:

"Many lines of evidence point to the atherogenic potential of lipoprotein remnants. Although no single finding confirms remnant lipoproteins as independent risk factors, circumstantial evidence is strong.… Several assays are available for identification and measurement of remnant lipoproteins; these include ultracentrifugation, electrophoreses, and immunological techniques. Remnant-like particles measured immunologically appear to be promising risk predictor. Even so, prospective studies relating various remnant measures to CHD risk are limited, and measurement with specific assays cannot be recommended for routine practice. Nonetheless, ATP III identified elevated VLDL cholesterol as the surrogate for elevated atherogenic remnants in persons with triglycerides > 200 mg/dL."

Regarding the role of remnant lipoproteins as a diagnostic technique for type III hyperlipoproteinemia, at this time, the diagnosis is based on genotyping or phenotyping apolipoprotein E. Furthermore, treatment of this disorder is based on LDL cholesterol and triglyceride levels, as described.

2004-2005 Update

A literature search for the period of 2003 through June 2005 did not identify any published articles that would address the limitations noted. Therefore, the policy statement is unchanged. Intermediate density lipoproteins continue to be included as intermediate outcome measures in controlled trials, and are a focus of studies examining lipid metabolism. (8-10) However, no studies directly examined how measurements of intermediate density lipoproteins can be used to improve patient management. In 2005 Tzou and colleagues examined the clinical value of “advanced lipoprotein testing” in 311 randomly selected adults participating in the Bogalusa Heart Study. (11) Advanced lipoprotein testing consisted of subclass patterns of LDL, lipoprotein(a) cholesterol, intermediate density lipoprotein cholesterol, high density lipoprotein cholesterol subclasses, and very low density lipoprotein subclasses. These measurements were used to predict the presence of subclinical atherosclerosis, as measured ultrasonographically by carotid intima-media thickness. In multivariate logistic regression models, substituting advanced lipoprotein testing for corresponding traditional lipoprotein values did not improve prediction of the highest quartile of carotid intima-media thickness.

In July 2004, Grundy and colleagues published an article outlining the implications of recent clinical trials of statin therapy. (12) The authors recommended a further lowering of the target LDL-C for some populations of patients. For example, the LDL-C target of 100 mg/dL in high-risk patients was lowered to 70 mg/dL. In addition, the authors recommend that consideration be given to combining a fibrate or nicotinic acid with an LDL-lowering drug in patients with high triglycerides or low HDL-C concentration. For moderately high-risk patients, the target LDL-C has been lowered from 130 mg/dL to 100 mg/dl. While not an explicit update of the ATP III recommendations, the conclusions were endorsed by the National Heart, Lung, and Blood Institute, the American College of Cardiology Foundation, and the American Heart Association. These new more aggressive targets of therapy create additional questions of how measurements of intermediate density lipoproteins can be used to improve patient management.

2006-2007 Update

A literature search was performed for the period of July 2005 through December 2006. One study examined the predictive ability of remnant-like particles for cardiovascular events. (13) Another explored the relationship between remnant-like particles and triglyceride levels. (14) These studies do not prompt reconsideration of the policy statement, which remains unchanged.

2008 Update

A literature search was performed for the period of January 2007 through March 2008. The majority of publications identified during this period focused on the pathophysiology and basic science aspects of IDL, with a smaller number of research studies reporting data with potential clinical relevance. There were no prospective, large-scale cohort studies that evaluated IDLs as a predictor of cardiovascular risk, nor were there any large diagnostic studies that evaluated the utility of IDLs in diagnosing type III hyperlipidemia.

A few small to moderate-sized cross-sectional studies evaluated IDLs as a predictor of cardiovascular risk. The largest study compared 126 women without CAD to 256 women with CAD (15). IDL levels were higher in patients with CAD, and the IDL level was positively correlated with the extent of CAD on angiography. Nakajima and co-workers (16) compared IDL levels in 165 Japanese patients with sudden cardiac death (SCD) with 93 patients who had died of other causes. IDL levels were higher in patients with SCD compared with non-SCD patients (median 81 vs. 49, p<0.001). In patients with CAD, there was a weak correlation between LDL-C and IDL levels (r=0.232). A third cross-sectional study (17) examined 64 patients who had undergone successful percutaneous coronary interventions (PCI) and stenting, 15 of whom had in-stent stenosis and 49 without restenosis. Patients with in-stent stenosis had higher IDL levels compared to patients without restenosis (8.2 +/- 7.0 mg/dL vs. 4.5 +/- 2.6 mg/dL, p=0.006). In multivariate analysis, an IDL level above the 75th percentile was the strongest independent predictor of restenosis (OR 8.15, 95% CI: 1.02–65.16, p=0.048).

Two small cross-sectional studies provided evidence on the potential utility of IDL level in diagnosing familial hypercholesterolemia (18,19). Both of these studies compared IDL levels in patients with familial hypercholesterolemia to patients without familial hypercholesterolemia. IDL levels were higher in patients with familial hypercholesterolemia compared to controls in both instances. However, neither study provided further clinically useful data such as the sensitivity and specificity of the test and/or the optimal threshold values for discriminating between patients with and without familial hypercholesterolemia.

None of the available studies provides guidance on the clinical use of IDL measurements, nor does this evidence suggest that health outcomes are improved as a result of measuring IDL level. As a result, this new evidence does not prompt reconsideration of the current policy, which remains unchanged.

2013 Update

A search of peer reviewed literature through July 2013 identified no new clinical trial publications or any additional information that would change the coverage position of this medical policy.

Coding

Disclaimer for coding information on Medical Policies

Procedure and diagnosis codes on Medical Policy documents are included only as a general reference tool for each policy. They may not be all-inclusive.

The presence or absence of procedure, service, supply, device or diagnosis codes in a Medical Policy document has no relevance for determination of benefit coverage for members or reimbursement for providers. Only the written coverage position in a medical policy should be used for such determinations.

Benefit coverage determinations based on written Medical Policy coverage positions must include review of the member’s benefit contract or Summary Plan Description (SPD) for defined coverage vs. non-coverage, benefit exclusions, and benefit limitations such as dollar or duration caps.

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